Method of heat treating magnetic iron to restore its magnetic properties



Sept. 7, 1954 ETAL J. 5. LEE METHOD OF HEAT TREATING MAGNETIC IRON TO RESTORE ITS MAGNETIC PROPERTIES Filed NOV. 13, 1950 mono En A650 DIG-x".

He A650 Mr (l/VAGED IJO DEGREES CENT/684D! PAUL.

JON THAN 5. LEE

Ff ELARDE.

Patented Sept. 7, 1954 METHOD OF HEAT TREATING MAGNETIC IRON TO RESTORE ITS MAGNETIC PROP- ERTIES Jonathan S. Lee, Downers Grove, and Paul F. Elarde, Westchester, Ill., assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application November 13, 1950, Serial No. 195,206

3 Claims.

The present invention relates to a method of treating aged magnetic iron to improve the magnetic quality thereof and more particularly to a method of heat treating aged magnetic iron to restore the magnetic quality thereof to its preaged condition.

It is well known that the magnetic properties of magnetic iron parts in electrical apparatus change with time due to the magnetic aging thereof and that the rate of aging of the magnetic iron parts increases with a rise in temperature which in most electrical equipment occurs as a result of the frequent use thereof. In the magnetic iron cores and armatures in telephone relays, aging detrimentally affects the magnetic qualities of the iron, as for example, by progressively increasing the coercive force and residual magnetism therein, which necessitates the frequent adjustment of the contact springs of the relay in order to maintain the relay in an operative condition. Aging may continue to the extent where the changes in the magnetic qualities of the iron exceed the point Where the springs can be adjusted to compensate for it, as for example, the residual magnetism in the iron parts may increase to the point where the armature after being attracted to the core sticks thereto even after the magnetizing current has been interrupted, thus rendering the relay unsatisfactory for further use.

It is an object of the present invention to provide a method of treating aged magnetic iron to improve the magnetic properties thereof.

A further object is to provide a simple method of heat treating the magnetic iron core of an assembled relay which has aged to restore the magnetic quality of the core to its pre-aged values without removing the core from the relay.

In accordance with one method of practicing the present invention to improve the magnetic properties of aged magnetic iron, the magnetic iron is subjected to heat and the temperature thereof is raised to a value of between 150 and 221 0., preferably 221 C for a short period of time to effect the restoration ofthe magnetic properties of the iron to its pre-aged condition. The magnetically aged iron core of the relay in an assembled condition may be connected in series with a secondary of a welding transformer and a relatively high current passed through the core for a short time to heat the core to approximately 200 220 C. to restore the magnetic properties of the core substantially to their original value without removing the core from the relay and without damaging the relay.

Other objects and advantages will become apparent by reference to the following detailed description of the invention and the accompanying drawing in which Fig. 1 is a graph showing in dotted lines the eifects of temperature on residual induction Br, and coercive force He, in an un-aged sample of magnetic iron, and in full lines the effects of temperature on Br and He in an aged sample of magnetic iron; and I Fig. 2 is a diagrammatic view of a device for electrically heating the core of a relay.

With the object of devising ways of overcoming the detrimental magnetic effects of aging and of restoring the magnetic properties of aged magnetic iron to their pre-aged condition, experiments' were conducted to determine the efi'ect of temperature upon the magnetic qualities of magnetic iron. An annealed ring sample of un-aged magnetic iron having a low carbon content of less than .04% was measured to determine the values of various magnetic properties thereof in its un-aged condition.

The ring sample of magnetic iron was then placed in an oven and subjected to successively increasing temperatures and by means of a test set connected to the ring, readings of magnetic induction B, in gausses, residual induction Br, in gausses, and coercive force He in oersteds (at 27 oersteds), were taken at various temperature levels at and above room temperature and at various magnitudes of magnetizing field H in oersteds. The value 11970 of Br at room temperature or 30 C. progressively decreased with progressive increases in temperature to a value of 10280 at approximately 210 C. as indicated in the dotted curve Br in Fig. 1. The value of E0 of the ring sample decreased from .869 to 30 C. to .698 at 210 C. as indicated in the dotted curve He in Figure 1. The ring sample Was then allowed tocool to room temperature and the I values of Br and He .Were again measured and found to be the same as they were before being subjected to the elevated temperatures.

The ring sample of magnetic iron was then artificially aged by subjecting it to a temperature of approximately C. for a period of 216 hours which artificial aging effect is equivalent to the natural aging occurring at normal room temperatures over a period of from three to six years. The sample was then cooled to room temperature and remeasured as before to determine the values of the various magnetic characteristics thereof after aging. It was found that the values of Br of the aged sample at 30 C. had

3 risen to 13390 and the value of He at 30 C. had risen to 1.70. The sample ring of magnetic iron was then placed in the oven and again heated to progressively increasing levels of temperature and again the readings of the furnace temperature were taken at these levels and the values of the magnetic characteristics were determined. The ring sample was demagnetized immediately before taking readings at each temperature level and it was permitted to remain fifteen minutes at the next temperature level to insure that all parts of the sample were uniformly heated to the desired temperature before measurements were made at the new level. As the ring sample was heated to progressively higher temperature levels the values of both Br and He fell to progressively Table 2.Sample at 30 C. after aging had the following characteristics:

15 Table 3.-Aged sample at various temperature levels had the following characteristics:

lower levels until the temperature reached the range of substantially 2l0--22'5 C. at which range the values for Br and He of the aged and the un-aged ring samples substantially coincided, indicating that the magnetic characteristics of Br and He in the aged ring sample of magnetic iron had been restored to the values of the u'rr-aged ring sample of magnetic iron. The sample ring was then cooled to room temperature and the magnetic properties of the de-aged ring sample were again measured and compared with those of the un-aged ring sample at room temperature and were found to be substantially the same. The heating of a ring sample was not continued beyond the point where the magnetic properties 'of the heated aged sample were substantially the same as those of heated un-age'd sample because "further heating to higher temperatures would be of no avail.

In checking the parts measurements were made of the magnetic induction of a sample at various temperatures and for different magnetizing forces as follows:

Table 1.--Un-aged sample at various temperature levels.

Table 4.De-aged sample at 30 C. had the following characteristics:

168C. 188C. 210C.

Since 27'oersteds is considered bymost of those working in the field as a satisfactory saturation point, the residual induction Br, and the-coercive force He, were taken at 27 oersteds and are as follows:

more complex Where the magnetic ir on parts are in assembled relation with other par-ts =of electrical apparatus and it is not feasible to remove the magnetic iron parts from the apparatus. After some investigation, however, it has been 11,-s0011,110 11,580 11,370 11,120 st .858 .808 .771 .752.

found that some of the magnetic iron parts formin components of electrical apparatus may be heated to the desired temperature by passing an electrical current therethrough without damaging the other parts such as the insulation on the wire and other components associated therewith. For example, aged magnetic iron cores of telephone relays may be de-aged to restore the electrical properties to their pre-aged condition by passing an electrical current of predetermined intensity and duration through the cores to heat the cores to a temperature of approximately 200-220 as previously mentioned.

In Fig. 2 of the drawing there is shown a diaerammatic view of a fixture It! for use in heating the magnetic iron core l l of a telephone relay The fixture comprises a base of insulating mate rial It on which is mounted in spaced relation to each other a pair of metal mounting lugs or supports I6 and is which are adapted to engage opposite end portions of the core H for support ing the relay i2. An L shaped bracket 2? welded to one end of the core i i is secured to the mounting lug It by a screw 2! and the opposite end of the core A! is clamped to the mounting lug is by a clamp 2t. Leads and 2% connect the lugs l6, l8 and the core It in a heating circuit including a secondary iii! of a step down transformer 32. The primary 33 of the transformer is connected to a suitable source of alternating current through a control unit 35 which controls the duration of the current during the heating operation.

Thus when the magnetic core of a relay has become aged to a point where it is no longer useful, in order to de-age the core to restore the magnetic properties thereof to its p-re-aged condition, it is merely necessary to apply the relay to the fixture l0 and connect the ends of the core H to the mounting lugs l6 and I8, after which the control unit 35 may be actuated to initiate a heating cycle of a predetermined duration to pass a predetermined relatively high current through the core H of the relay and raise the temperature thereof to approximately 200- 220 C. The heating or the core H of the relay is of such short duration as to leave the coil and spool parts associated therewith undamaged While effectively improving the magnetic properties thereof and r storing them to their pre-aged condition. It was found that heating the aged magnetic iron core of a relay for approximately two minutes at a temperature of approximately 205 0. without removing the core from the relay, was effective in restoring the magnetic qualities of the core to substantially their pre-aged or original values. It will be understood that the intensity and duration of the current applied to the core may vary to heat the core to the desired temperature without damaging the other parts of the relay.

It is to be understood that the above-described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. A method of treating an iron core of an electro-magnetic relay which has lost some of its magnetic properties due to aging to restore the magnetic properties thereof to that of the core before agin without removin the core from the relay, which method consists of connecting the magnetic iron core to an electric circuit and passing a relatively high current therethrough to raise the temperature of the core to approximately 205 C., maintaining said core at 205 C. for approximately two minutes, and cooling the core to room temperature.

2. A method of treating an iron core of an electro-magnetic relay which has lost some of its magnetic properties due to aging to restore the magnetic properties thereof to that of the core before aging without removing the core from the relay, which method consists of connecting the magnetic iron core to an electric circuit and passing a relatively high current therethrough to raise the temperature of the core to approximately 295 C. for a length of time sufficient to insure that all parts of the core have attained said temperature, and cooling the core to room temperature.

3. A method of treating an iron core of an metro-magnetic relay which has lost some of its magnetic properties due to aging to restore the magnetic properties thereof to that of the core before aging without removing the core from the relay, which method consists of connecting the magnetic iron core to an electric circuit and passing a relatively high current therethrough to heat the core to a temperature of between and 221 C. for a length of time sufficient to insure that all parts of the core have attained said temperature, and cooling the core to room temperature.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 432,651 Thomson July 22, 1890 1,373,969 Milton May 24, 1921 1,715,713 Legg June 4, 1929 2,044,763 Bouton et al June 23, 1936 2,401,733 Green June 11, 194:6

OTHER REFERENCES Cleaves and Thompson: The Metal Iron published by McGraw-Hill Book. Co., New York, 1935, page 431. 

1. A METHOD OF TREATING AN IRON CORE OF AN ELECTRO-MAGNETIC RELAY WHICH HAS LOST SOME OF ITS MAGNETIC PROPERTIES DUE TO AGING TO RESTORE THE MAGNETIC PROPERTIES THEREOF TO THAT OF THE CORE BEFORE AGING WITHOUT REMOVING THE CORE FROM THE RELAY, WHICH METHOD CONSIST OF CONNECTING THE MAGNETIC IRON CORE TO AN ELECTRIC CIRCUIT AND PASSING A RELATIVELY HIGH CURRENT THERETHROUGH TO 